IceCube detects high-energy extraterrestrial neutrinos

21 November 2013

IceCube provides first evidence for high-energy neutrinos of astrophysical origin

The IceCube Neutrino Observatory, a giant particle detector buried in the Antarctic icecap, is a demonstration of the power of the human passion for discovery, where scientific ingenuity meets technological innovation. Today, nearly 25 years after the pioneering idea of detecting neutrinos in ice, the IceCube Collaboration announces the observation of 28 very high-energy particle events that constitute the first solid evidence for astrophysical neutrinos from cosmic accelerators. Details of the research are published in Science 342 (2013) 1242856.

The 28 high-energy neutrinos were found in data collected from May 2010 to May 2012 and analyzed for neutrino events that exceed 50 teraelectronvolts (TeV) and come from anywhere in the sky. Two of the events have energies exceeding 1000 TeV (Physical Review Letters 111 (2013) 021103). The events cannot be explained by other neutrino fluxes, such as those from atmospheric neutrinos (produced by the interaction of cosmic rays in the atmosphere).

IceCube is comprised of 5160 'digital optical modules' suspended along 86 strings embedded in a cubic kilometer of ice beneath the South Pole. It detects neutrinos through the flashes of blue light, called Cherenkov radiation, produced when neutrinos interact in the ice. The detector was completed in December 2010 after seven years of construction.

The IceCube Neutrino Observatory was built with funding from the National Science Foundation, USA, with assistance from partner funding agencies around the world. The University of Wisconsin–Madison is the lead institution, and the international collaboration includes 250 physicists and engineers from the USA, Germany, Sweden, Belgium, Switzerland, Japan, Canada, New Zealand, Australia, UK and Korea.

The University of Oxford is the only UK participant and is represented by Professor Subir Sarkar of the Rudolf Peierls Centre for Theoretical Physics. "It may seem surprising to see a theorist involved in an experiment such as this" he said, "But modern experiments do need state-of-the-art theoretical input. Our contribution to this analysis was the calculation of precise cross-sections for the 'deep inelastic scattering' of high energy neutrinos, drawing on the work of our colleagues in the Particle Physics sub-department who have made the most precise measurements of the relevant parton distribution functions at the HERA accelerator in Hamburg".

So far the events are consistent with being from either galactic sources (e.g. supernova remnants) or extragalactic sources (e.g. active galactic nuclei or gamma-ray bursts). However as more data is accumulated the sources will be pinpointed and this finding will be seen to mark the birth of a new astronomy ... not with photons but with neutrinos - revealing a previously unseen high energy universe.

IceCube has also recently detected the quantum mechanical oscillations of atmospheric neutrinos (Physical Review Letters, 111 (2013) 081801). The proposed 'Precision IceCube Next Generation Upgrade' (PINGU) will make high statistics measurements that may answer key questions in fundamental neutrino physics.